Method for producing a blank, blank and a dental restoration

ABSTRACT

The invention relates to a blank of a ceramic material, wherein a first ceramic material and then a second ceramic material of different compositions are filled into a die and wherein the materials are pressed and after pressing are sintered. A layer of the first ceramic material is thereby filled into the die and a first cavity formed in the layer, the second ceramic material is then filled into the first open cavity and the materials pressed together and then heat-treated.

THE CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of patent application U.S. Ser. No.15/388,282, filed on Dec. 22, 2016, which claims the benefit of andpriority to German Patent Application No. 10 2015 122 861.0, filed onDec. 28, 2015, which are herein incorporated by reference for allpurposes.

TECHNICAL FIELD

The invention relates, inter alia, to a method for the preparation of ablank of a ceramic material, in particular a blank to be used for thepreparation of a dental restoration, wherein a first ceramic materialand then a second ceramic material of different compositions are filledinto a die and wherein the materials are pressed and after pressing aresintered.

The invention also relates to a pre-sintered or fully-sintered blank tobe used for the preparation of a dental restoration, such as a dentalframework, crown, partial crown, bridge, cap, veneer, abutment, pinconstruction, in particular a crown or partial crown, comprising aceramic material which in particular contains zirconium dioxide and hasregions of different compositions.

BACKGROUND

U.S. Pat. No. 8,936,848 B2 discloses a blank of zirconium dioxide thatis used for the preparation of a tooth replacement and comprises anumber of layers of different chemical compositions. The individuallayers thereby have different percentages of yttrium oxide.

A body of zirconium dioxide exhibits a decrease or increase inchromacity along a straight line in the L*a*b* color space (US2014/0328746 A1).

A blank of zirconium dioxide for the preparation of dental objects inaccordance with WO 2014/062375 A1 has at least two material regionswhich have different percentages of tetragonal and cubic crystal phases,wherein in one of the regions the quotient is greater than 1 and in theother region the quotient is lower than 1.

EP 2 371 344 A1 relates to a ceramic body which is enriched with astabilizing agent from the surface to a desired depth.

Zirconium dioxide is used as a ceramic material to produce dentalrestorations. A framework can be milled, for example, from a blank ofzirconium dioxide and can then be sintered. In the following processingstages, a veneer is applied manually to the framework, wherein at leastone incisor material is applied and fused. All of these process measuresare time-consuming and moreover do not ensure that the dentalrestoration will meet the requirements.

SUMMARY OF THE INVENTION

It is an object of the present invention to develop a method of theaforementioned type in such a way that the disadvantages of the priorart are avoided and in particular that a dental restoration can beproduced from a ceramic material without laborious finishing, whichsatisfies aesthetic requirements and moreover is of high strength inregions under severe loads.

To achieve this aim it is proposed, inter alia, that a layer of a firstceramic material is filled into the die and that a first open cavity isformed in the layer, that the second ceramic material is filled into thefirst open cavity and that the materials are pressed together and arethen heat-treated.

According to the invention, a layer of pourable material is first filledinto a die. This may, for example, be a colorless zirconium dioxidegranular material that has a bulk density between 1 g/cm³ and 1.4 g/cm³,in particular in the region between 1.15 g/cm³ and 1.35 g/cm³. Followingfilling of the granular material, which has a grain size D50 between 40μm and 70 μm, an open cavity is formed, for example by means of a pressplunger. This is carried out, for example, by expelling parts of thefirst ceramic material and/or lightly compacting them. Thus, in theso-formed recess or cavity, which in particular has a substantiallyconus-like geometry, the second ceramic material is filled, if a crownor partial crown is to be produced from the blank, the conus-like shapedrecess or cavity is aligned with the geometry of a tooth stump or anabutment, so that the materials are pressed together.

There is also the possibility of forming a further, second open cavityin the second ceramic material that fills the first open cavity. Thisstep can accompany the concomitant pressing of all materials.

Compaction of the materials takes place independently thereof.

Compression is preferably carried out at a pressure preferably between1000 bar and 2000 bar. A density of approximately 3 g/cm³ is attained.Debinding and pre-sintering at a temperature between 700° C. and 1100°C. are then carried out, in particular in a range between 800° C. and1000° C., over a time between 100 minutes and 150 minutes.

The debinding and pre-sintering should be carried out in such a way thata breaking strength between 10 MPa and 60 MPa, in particular between 10MPa and 40 MPa is achieved, measured in accordance with DIN-ISO 6872.

Where a second open cavity is formed in the second ceramic material anda third ceramic material is filled into it, then this composition shoulddiffer from that of the second ceramic material, in particular in havinga lower translucence and/or a higher bending strength than thesecond/first material.

In particular, according to the invention a number of first opencavities are provided in the layer of the first ceramic material, andthe second ceramic material is filled into these. This yields a numberof distinct, separated blank sections, so-called nests, so that afterthe pre-sintering a number of dental restorations can be derived fromthe sections of such a blank, in particular through milling and/orgrinding. Thereby it is possible for the dimensions of the blanksections to differ from one another to derive restorations of differentgeometries which can also differ in the geometric arrangement of therespective root-side/dentine-side material regions. It is thereforepossible to obtain teeth of different shapes from one blank, accordingto the number of nests/blank sections and their geometries. As alreadymentioned, the dentine cores are formed from the second regions and theincisors from the first region.

The invention in particular provides for the thermal expansioncoefficient of the second ceramic material to be 0.2 μm/m*K to 0.8μm/m*K higher than the thermal expansion coefficient of the firstceramic material. As a result of the different thermal expansioncoefficients of the materials, a compressive stress is created in thefirst material i.e. in the incisor material which leads to an increasein strength of the dental restoration derived from the blank.

Furthermore, there is the possibility of coloring the ceramic materialsto the desired extent, in particular such that for the first region anincisor material is used which is more translucent and less coloredcompared to the second ceramic material.

If a dental restoration or other molded body is preferably derived fromthe pre-sintered blank, then there is naturally also the possibilitythat the blank is first fully-sintered to then produce the molded body,in particular by milling or grinding.

Independently of when the blank is sintered through, it is provided inparticular for the complete sintering to be carried out over a period ofbetween 10 minutes and 250 minutes at a temperature in the range between1300° C. and 1600° C. Sintering may also be carried out at a slightlyhigher temperature.

If sintering is performed at a temperature which, for example, is 100°C. above the temperature given by the manufacturer of the startingmaterial, and above the time recommended by the manufacturer for thecomplete sintering, this is referred to as over-sintering.

The present values apply in particular when the starting materialsubstantially contains zirconium dioxide, in particular more than 80 wt%.

Yttrium oxide is in particular added to the zirconium dioxide, butcalcium oxide, magnesium oxide and/or ceroxide may also be added.

If the ceramic material is colored, then in particular a color-impartingoxide from elements of the group Pr, Er, Tb, Fe, Co, Ni, Ti, V, Cr, Cu,Mn, preferably Fe₂O₃, Er₂O₃ or Co₃O₄ is used.

The invention is therefore also characterized by the fact that theceramic materials used contain zirconium dioxide to which is addedyttrium oxide (Y₂O₃), calcium oxide (CaO), magnesium oxide (MgO) and/orcerium oxide (CeO₂), in particular yttrium oxide, wherein the firstceramic material differs from the material of the second ceramicmaterial in terms of color and/or crystal forms stabilized at roomtemperature.

Further, it is provided for the first and/or second ceramic material tobe such that the percentage of yttrium oxide in the second material isin the range 4.5 wt % to 7.0 wt % and/or the percentage in the firstmaterial is in the range 7.0 wt % to 9.5 wt %, wherein the percentage ofyttrium oxide in the first ceramic material is higher than that in thesecond material.

The materials of the first and also the second region should thereby beselected such that the quotient of the tetragonal crystal phase to thecubic crystal phase of zirconium dioxide of both regions afterpre-sintering is 1.

The following composition in wt % is preferred as the basic material forthe first and second ceramic material:

HfO₂ <3.0 Al₂O₃ <0.3 Technically caused, unavoidable components ≤0.2(e.g., SiO₂, Fe₂O₃, Na₂O) For the first layer: Y₂O₃ 7.0 to 9.5 For thesecond layer: Y₂O₃ 4.5 to 7.0 Coloring oxide: 0-1.5 ZrO₂ = 100 − (Y₂O₃ +Al₂O₃ + HfO₂ + unavoidable components + color-imparting oxides)

It is also possible for additional binding agents to be added. This isnot taken into account in the above statement of percentage by weight.

According to the teaching of the invention, after full sintering amonolithic dental restoration is obtained, which in principle does nothave to be veneered, but if so then there is no departure from theinvention.

A pre-sintered or fully sintered blank for use in producing a dentalrestoration such as a dental framework, crown, partial crown, bridge,cap, veneer, abutment, pin construction, in particular crown or partialcrown, consisting of a ceramic material, which in particular containszirconium dioxide and regions of different compositions, wherein a firstregion is of a first ceramic material and at least one second region isof a second ceramic material and the regions are adjacent to each other,is characterized by the fact that at least one second region extendswithin the first region and has an outer geometry that tapers from abasal region. Thereby, the basal region should extend in the region ofan outer surface of the first region, and preferably merge with it.

It is also possible for the second region extending from the basalregion to have a cavity.

Independently of this, the second region in its outer geometry has aconus-like extending geometry.

There is also the possibility that a third region extends within thesecond region, said third region consisting of a third ceramic materialof a composition which deviates from that of the second ceramicmaterial.

It is to be emphasized and in accordance with this invention that anumber of second regions are surrounded by the first region, inparticular some of the plurality of second regions differ in theirexternal geometries.

Thus, for example, crowns or artificial teeth of different geometriescan be produced, which have a higher strength in the dentine than in theincisal region. For this purpose upon derivation of the dentalrestoration from the blank, the dentine is formed in the region ofsections of the second region and the incisal region is formed fromsections of the first region of the blank.

The invention is further characterized in that the blank containszirconium dioxide to which yttrium oxide has been added, that thepercentage of yttrium oxide in the second or third ceramic material liesbetween 4.5 wt % and 7.0 wt % and in the first ceramic material liesbetween 7.0 wt % and 9.5 wt %, wherein the percentage of yttrium oxidein the first ceramic material is greater than in the second ceramicmaterial.

The lower yttrium content in the material of the second region resultsin a higher strength in comparison to that of the first region.

Furthermore, there is the possibility that the ceramic material of thesecond region is colored and that of the first region is colored to alesser degree or not at all, so that a higher translucency than in thesecond region results.

A dental restoration, in particular tooth, crown or partial crown, ischaracterized by comprising a first layer of a first material whichextends on the incisial side and a root side-extending second layerconsisting of a second ceramic material, in that the first layer has ahigher translucency and/or a lower strength than the second layer andthat the first layer has a thermal expansion coefficient of about 0.2μm/m*K to 0.8 μm/m*K lower than that of the second layer.

Further details, advantages and features of the invention result notonly from the claims and the features disclosed therein alone and/or incombination but also from the following description of the exampleembodiments shown in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1a shows a schematic of a device and a process step of the presentinvention performed using the device,

FIG. 1b shows a schematic of another process step of the presentinvention performed using the device shown in FIG. 1 a,

FIG. 1c shows a schematic of another process step of the presentinvention performed using the device shown in FIGS. 1a and 1 b,

FIG. 2 shows FIG. 1b in greater detail,

FIG. 3 shows a blank according to the present invention with regions ofdifferent material properties,

FIG. 4 shows another blank according to the present invention withregions of different material properties,

FIG. 5 shows a schematic of a blank according to the present inventionwith a tooth to be derived therefrom, and

FIG. 6 shows a blank according to the present invention in a top viewwith a plurality of regions of different material properties.

DETAILED DESCRIPTION OF THE INVENTION

The teaching of the invention is illustrated by reference to thefigures, in which the same elements are basically given the samereference numerals, wherein in particular dental restorations areproduced from a ceramic material having a monolithic structure such thatafter complete sintering an immediately usable monolithic toothreplacement is available.

To this end, the invention provides for the preparation of a blank,which has regions of ceramic material with differing compositions andthus properties, has desired optical and mechanical properties accordingto the restoration to be produced, which, as mentioned, offer thepossibility of immediate usage of the tooth replacement monolithicallyfabricated after full sintering without, for example, having to applyincisor material by hand.

Further, specifically desired strength values are attainable in theranges in which high loads occur. Desired optical properties can beachieved.

With reference to FIGS. 1 to 3, the manufacture of a blank will bedescribed from which a dental restoration can be produced, in theexample embodiment, a tooth.

Thus a pourable granulate in the form of a first ceramic material 14 isfilled into the die 10 of a pressing tool 12, which is in particular azirconium dioxide stabilized with yttrium oxide, which can have thefollowing composition in wt %:

HfO₂ <3.0 Al₂O₃ <0.3 Y₂O₃ 7.0 to 9.5 Color-imparting oxides: 0-0.5Technically caused, unavoidable components ≤0.2 (such as SiO₂, Fe₂O₃,Na₂O) ZrO₂ 100 − (Y₂O₃ + Al₂O₃ + HfO₂ + color-imparting oxides +technically caused, unavoidable components)

A binding agent may also be added, but is not taken into considerationin the above percentage by weight values.

However, in particular it is provided for the composition to containcoloring oxides only in small amounts or not at all, for example ≤0.5 wt%, as the first ceramic material 14 is used as an incisor material, sothat a high translucency is desired. As a result of the relatively highpercentage of yttrium oxide, the tetragonal crystal phase is only 50 to60% in the incisal region of the produced mold part, i.e., the dentalrestoration, and the remainder is the cubic and monoclinic crystalphase.

Then, by means of a press plunger 16 an open cavity 18 is formed in amaterial 14 or in a layer formed from this material. By means of thepress plunger, the material 14 is displaced or slightly compacted. Afterthe cavity 18 is formed (FIG. 1b ), the press plunger 16 is removed anda second ceramic material 20 filled into the cavity 18, which may haveone of the following compositions in wt %:

HfO₂ <3.0 Al₂O₃ <0.3 Y₂O₃ 4.5 to 7.0 Color-imparting oxides: 0-1.5Technically caused, unavoidable components ≤0.2 (such as SiO₂, Fe₂O₃,Na₂O) ZrO₂ 100 − (Y₂O₃ + Al₂O₃ + HfO₂ + color-imparting oxides +technically caused, unavoidable components)

Thereby, the coloring oxide or oxides should be present in an amountthat results in a desired tooth color, since the dentine of the tooth tobe produced is formed from the second ceramic material 20. Therelatively low percentage of Y₂O₃ further ensures that the dentine ofthe fully-sintered tooth replacement has a high tetragonal phase contentof at least 85%, preferably at least 90%, thus yielding a high strength.

After filling of the second ceramic material 20 into the cavity 18 (FIG.1c ), the materials 14, 20 respectively the layers or regions formedfrom these, are pressed in the die 10 by means of a lower or upper punch22, 24 through which a compaction results. After pressing, the blank 28has a density of approximately 3 g/cm³. Pressing is preferably carriedout at a pressure between 1000 bar and 2000 bar.

With regard to the ceramic materials 14, 20 it should also be noted thatthey have a bulk density between 1 g/cm′ and 1.4 g/cm³. After pressing,the density is approximately 3 g/cm³.

FIG. 2 shows the contents of FIG. 1b ) in more detail. It can be seenthat the cavity 18 is formed through the press plunger 16 in the firstceramic material 14 respectively in the layer comprising the material.On the base side the die 10 is limited by the press plunger 22.

As can be seen from FIG. 3, a second cavity 26 can be formed in thesecond material 20 after its compression by the press plunger 22, 24 oroptionally after the pre-sintering, for example by milling.

However, in accordance with FIG. 1c ), it is also possible to form acorresponding second cavity 26 in the material 20, which completelyfills the bottom-side open cavity 18, by means of a press plunger thatis not shown.

Irrespective of whether the second cavity 26 is present or not, apre-sintering of the blank 28 is carried out after pressing at atemperature in particular in the range between 800° C. and 1000° C. overa time period between 100 minutes and 150 minutes. There is initially adebinding and then pre-sintering. The density of the blank 28 after thepre-sintering is approximately 3 g/cm³. The breaking strength of thepre-sintered blank 28 should be between 10 MPa and 60 MPa.

The blank 28 is provided with a holder 30, so that the blank 28 can beworked for example in a milling or grinding machine to derive a dentalrestoration such as a tooth from the blank 28, as explained withreference to FIG. 5. Thereby, the tooth to be produced is at leastvirtually laid in the blank 28 such that the incisal region runs intothe region 32 formed by the first ceramic material 14 and the dentineregion in sections runs into the second region 34 formed by the secondceramic material 20. The blank 28 is then worked taking this data intoconsideration.

FIG. 4 illustrates that after filling of the first cavity 18 in thefirst ceramic material 14 and filling of the second ceramic material 20into the cavity 18, a second cavity 36 is filled optionally inaccordance with the procedure of FIG. 1b ), so that a third ceramicmaterial is filled into the cavity 36 so formed, which differs from thesecond ceramic material in its composition such that in particular ahigher strength can be achieved. A cavity 40 may similarly be formed inthe third ceramic material 38—as explained with reference to FIG. 3.

As FIG. 5 illustrates, a dental restoration, in the example embodiment,a tooth 42, is derived from the blank 28. For this purpose, withknowledge of the course of the first region 32 from the first ceramicmaterial 14 and the second region 34 from the second ceramic material 20in the blank 28 of the tooth 42 to be produced is virtually laid in theregions 32, 34 such that the incisor extends in the first region 32 andthe dentine 46 extends into the second region 34.

After removal of the so virtually positioned tooth 42 from the blank 28,a tooth replacement is available, which in principle can be useddirectly, in particular does not require any veneer. A monolithic tooth42 is prepared on the basis of the teaching of the invention. In thiscase, the preparation from the blank 28 is made easier in that thesecond region 34 already has an open cavity 26, as described withreference to FIG. 3 and as apparent from FIG. 5.

The teaching of the invention introduces the possibility of forming ablank 48 that has a plurality of regions 52, 54, 56, that are made ofthe second and optionally the third ceramic material, and can havedifferent geometries (FIG. 6), so that corresponding teeth of differentgeometries can be formed. The so-called second regions 50, 52, 54 formedfrom the second ceramic material 20 are embedded in the first ceramicmaterial 48, i.e., are surrounded by this, as can be seen in particularalso from the Figures. The second regions 50, 52, 54 are uncovered onthe base side.

As can be seen in particular from FIGS. 2-4, the second regions haveexternal geometries that taper starting from the bottom, i.e., from thebase region. It may be referred to as a conus-like geometry, wherein theouter contour represents a freeform surface.

The base region 35/the base surface that limits it on the undersidemerges with the lower side of the base surface 33 of the first region32.

To prepare the blank sections 52, 54, 56 also referred to as nests, itis necessary as described with reference to FIG. 1 to have correspondingopen cavities in the layer made of the first material 14 and designatedas the first region 50, so that the pourable second ceramic material 20can be filled into the cavities in the manner described above and thenthe materials 14, 20 can be pressed together, i.e., compacted.

With regard to the physical properties of the materials 14, 20 it is tobe noted that in addition to a difference in translucency and strengththey should also have different thermal expansion coefficients. Inparticular, the invention provides for the first ceramic material 14after full sintering to have a thermal expansion coefficient that is 0.2μm/m*K to 0.8 μm/m*K lower than the second region 38, 52, 54, 56 formedfrom the second ceramic material 20. As a result of this a compressionstress is generated in the first region 50, i.e., in the incisormaterial, which leads to an increase in strength.

With regard to the blanks 28, 48 it is to be noted that these can have acuboid shape, for example the dimensions 18×15×25 mm or a disk shape,for example with a diameter of 100 mm, without thereby affecting theteaching of the invention. This brings in particular as explained byreference to FIG. 6 the advantage that, for example, a plurality ofsecond regions 52, 54, 56 so-called dentine cores can be formed in adisk-shaped blank, to yield restorations of different geometries, butwith a favorable layer course with respect to translucency and strength.

Since the position of one or more second regions 52, 56, i.e., nests,optionally with different geometries is known, they can be stored in adata record. Then, the restorations to be produced, which are availableas CAD data sets, are positioned relative to and in the blank sectionsso that the tooth replacement can be derived from the blank by millingand/or grinding.

1. A pre-sintered or fully-sintered blank for use in preparing a dentalrestoration, the blank comprising regions of different compositions,wherein one first region of a first ceramic material and at least onesecond region of a second ceramic material are of different compositionsand the regions are sited next to one another, wherein the ceramicmaterials contain zirconium dioxide doped with yttrium oxide (Y₂O₃),calcium oxide (CaO), magnesium oxide (MgO) and/or ceroxide (CeO₂), andwherein the first ceramic material differs from the material of thesecond ceramic material in terms of color and proportions of stabilizedcrystal forms present at room temperature, and wherein the at least onesecond region extends within the first region and has an externalgeometry that tapers from a base region or a base surface.
 2. The blankaccording to claim 1, wherein the base region or the base surface of theat least one second region extends in the region of an outer surface ofthe first region.
 3. The blank according to claim 1, wherein the atleast one second region starting from its base region or base surfacehas a cavity.
 4. The blank according to claim 1, wherein the at leastone second region has a conus-like geometry on its outer side.
 5. Theblank according of claim 1, wherein the at least one second regionincludes a third region extending at least partially therein, the thirdregion including a third ceramic material having a composition differentfrom that of the first and/or second ceramic material.
 6. The blankaccording to claim 1, wherein the at least one second region includes aplurality of second regions surrounded by the first region.
 7. The blankaccording to claim 6, wherein at least some of the plurality of secondregions differ from one another in their external geometries.
 8. Theblank according to claim 1, wherein the composition of the first,second, and/or third ceramic material includes zirconium dioxide towhich yttrium oxide has been added.
 9. The blank according to claim 8,wherein the percentage of yttrium oxide in the second or third ceramicmaterial lies between 4.5 wt % and 7.0 wt % and in the first ceramicmaterial between 7.0 wt % and 9.5 wt %, and wherein the percentage ofyttrium oxide in the first ceramic material is greater than in thesecond ceramic material.
 10. The blank according to claim 1, wherein thesecond ceramic material differs from the first ceramic material in beingcolored.
 11. The blank according to claim 1, wherein after fullsintering the restoration produced from the blank has a higher strengthon the dentine side than on the incisal side and/or on the incisal sidehas a higher translucency than on the dentine side.
 12. The blankaccording to claim 1, wherein the thermal expansion coefficient of thefirst region is 0.2 μm/m*K to 0.8 μm/m*K lower than the thermalexpansion coefficient of the second and/or third regions.
 13. A dentalrestoration prepared according to claim 1, wherein the restoration isformed monolithically and comprises at least one first layer extendingon the incisal side of a first ceramic material and a second layerextending on the dentine side of a second ceramic material, wherein thefirst layer has a higher translucency and/or lower strength than thesecond layer, and wherein the ceramic materials contain zirconiumdioxide doped with yttrium oxide (Y₂O₃), calcium oxide (CaO), magnesiumoxide (MgO) and/or ceroxide (CeO₂), and wherein the first ceramicmaterial differs from the material of the second ceramic material interms of color and proportions of stabilized crystal forms present atroom temperature.
 14. The dental restoration according to claim 1,wherein the thermal expansion coefficient of the first layer is 0.2μm/m*K to 0.8 μm/m*K lower than the thermal expansion coefficient of thesecond layer.